PHOTOINHIBITION AND LIGHT ACCLIMATION IN SEEDLINGS OF BISCHOFIA-JAVA']JAVANICA, A TROPICAL FOREST TREE FROM ASIA

The aim of this study was to examine the potential for light acclimation in shade grown seedlings of Bischofia javanica Blume. The seedlings were grown under simulated forest shade light (40 μmol m-2 s-1), and after transfer to a higher light level (1200 μmol m-2 s-1), chlorophyll fluorescence induction kinetics, net photosynthesis, and changes in leaf chlorophylls and leaf anatomy were examined in leaves that were fully developed prior to the transfer.The low-light (LL) leaf displayed photoinhibition immediately after transfer to high-light (HL). This photo-inhibition was substantial, and continued for several days. Chlorophyll bleaching occurred only after a certain degree of photoinhibition had proceeded. Photosynthetic light acclimation commenced immediately after severe photoinhibition. An increase in chlorophylls per unit leaf area was also immediate after severe bleaching. The changes in leaf chlorophylls over time were consistent with the visual observations of bleaching and recovery. The leaf weight per unit leaf area increased gradually on transfer to HL and finally it approached that of the newly formed HL leaf. Although fully expanded prior to transfer to HL, the leaf thickness was increased by about 45% and the leaf tissues became denser without changing the leaf area and the stomatal density. Finally, the net photosynthetic rate per unit leaf area was higher than that before exposure by 75% but less than that of newly formed HL leaf by more than 30%. Moreover, leaf movements were observed after exposure to HL and also the formation of short epicormic shoots with a cluster of small leaves on the lower part of the stem during light acclimation.It is concluded that the fully expanded shade leaf has a wide acclimation plasticity. In addition to leaf acclimation, whole plant responses such as leaf movements, the formation of epicormic shoots and the production of new 'sun-type' leaves under HL may be of crucial importance to the success of the species following opening of the canopy. © 1992 Annals of Botany Company.